1. Field of the Invention
This invention relates to automatic ranging systems and, more particularly, to an automatic ranging system in which range to an object is obtained by measuring parallax displacement in two TV stereo views of the object.
2. Background of the Invention
A number of ranging or distance measuring techniques presently exist that use RADAR or pulse-echo time of flight of a reflected RF signal. There are also other well-known cooperative RF distance measuring techniques such as DME that indicate range directly at the point of use, such as the cockpit of an aircraft, but the technique requires the use of a ground transponder in its operation. These RF systems are not passive and thus have grave limitations in military applications such as in tactical situations where radio silence is mandated. In addition, pulsed RADAR techniques have range limitations since electromagnetic radio waves move at a rate of approximately a foot for each nanosecond of elapsed time. Therefore, measuring down to ranges of a few inches or to an accuracy of fractions of an inch at a range of a few feet present problems with presently available equipment. There are phase-coherent RADAR systems that have the desired capability; however, the logic required to process a complete 3-D scene to identify and store x, y, z, or other coordinates for each object in the scene in almost real time presents formidable problems.
Range finders of the stereoscopic class, usually having an arrangement of optical elements such as mirrors or prisms constructed to give a rapid mechanical solution of a triangle having the target at its apex and the range finder at one corner of its base, are also well known in the prior art. With the advent of electrical transmission of visual scenes by wired or wireless systems, the technology has become available for the use of electronic means to extend the capabilities of rangefinding systems and reduce the number of expensive optical elements required for the purpose. Further, the use of electronic image forming means makes it possible to use frequencies of the electromagnetic spectrum outside the visual range. Because of these factors, development of stereoscopic range finders utilizing cathode ray TV tubes, image storage tubes, Charge Coupled Devices (CCD) solid-state imaging technology, and similar electronic image forming means, in their operation has been undertaken. The ranging system of the present invention is of the class of rangefinders utilizing stereoscopic electronic imaging technology.
Television combined with the power of digital processing systems that are commercially available at the present time make the approach of the present invention for ranging on objects in a viewed scene highly effective. Targets in a scene being ranged on can be completely passive and noncooperative and accuracy down to fractions of an inch are possible. Imaging systems commercially available from a number of manufacturers (such as Colorado Video, Inc., Hamanatsu, General Electric, and others) digitize video output for microprocessor manipulation.
For completely passive noncooperative ranging, two TV stereo views must be stored. If processing starts after the storage of both TV frames, assuming that both stereo TV frames are stored at the same time, an interval of 1/30 of a second will have elapsed. Even for relatively simple processing algorithms, fractions of a second to several seconds must be added to the 1/30 of a second TV frame acquisition time before range data is available.
The automatic ranging system of the present invention does not use a microprocessor for the range solution because it is too slow. However, a microprocessor is used to apply the range solution to a particular application. Logic functions in the system are served by conventional hard-wired TTL (transistor-transistor logic). Logic-circuits provide range data in less than 200 microseconds after a TV line is scanned. Range to every change of contrast in the common stereo scene is stored in a RAM (random access memory). The RAM address is the x-y coordinate of the range information. Therefore, x, y, and z coordinates to all objects in the scene are available for processing.
3. Description of the Prior Art
Stereoscopic ranging systems utilizing electronic image forming means are disclosed in the prior art by J. J. Redmann (U.S. Pat. No. 3,706,493) and R. Gerharz (U.S. Pat. No. 3,961,851). In Redmann, at least two optical systems whose axes are separated by a known distance contain lenses for focusing rays from a source onto an image retaining surface. Apparatus is provided for determining the angular position of the radiation source with respect to the optical systems axes such that the range of the source can be calculated. Gerharz discloses a system having at least three TV cameras in which the two TV cameras having the greatest baseline separation are utilized to produce superposed image frames. An electronic correlator makes use of the separation of two consecutive points in the superposed image frames to perform the range analysis function automatically.